Spray granulation

Fluidised bed spray granulation showcased by using the example of “pesticides”

Granulating creates free-flowing solids, directly from the suspension / solution.

Pesticides are often produced in the aqueous phase as a suspension. A dust-free product (application safety) must be created. Targeted grain structure results in granules in the desired grain size and optimal temperature control enables high chemical stability.

Fluidized bed spray granulation has become firmly established as a drying process in recent years, because it can convert a solid-containing liquid into a dry product in a single process step. Numerous advantages, such as

(1) the possibility of influencing the resulting particle size and bulk density
(2) the extremely precise control of product temperature as well
(3) the generally low process temperature contribute to this success.

A characteristic of the process is that the liquid is sprayed onto its own particles, which are intensively mixed and dried in the fluidized bed. As a result of the spraying, the particles grow. If you have exceeded a defined, adjustable size, they will be discharged. This creates a continuous process in which only liquid is added and only dry product is withdrawn.

Spray granulation is a convective drying process, i.e. energy is supplied via heated air. This also takes care of the evaporation of the water. The special feature of the process is the combination of spraying the liquid with drying in the fluidized bed. When spraying, the liquid is dispersed into fine droplets. This creates a large surface area. One liter of water can produce 15 billion droplets with a surface area of ​​120 m². These droplets are sprayed onto a fluidized bed, which also provides a very large surface for drying.

1
2
3
4
5
6
Wirbelschichttechnik
1
Spray drops
2
Particles
3

Air flow

4

Solidifying

5

Onion structure

6
finished granules

Further applications for fluidised bed spray granulation are:

  • Production of dust-free granulates (for liquids with a high solid content)
  • Drying at low temperatures.

Advantages of fluidised bed spray granulation are:

  • Top spray
  • Continuous operation
  • Drying and shaping in one step